Piston ring



Pstenied Dee. 12, i944 ns'roN 'RING Allen W.. Morton, Baltimore, Md., assis-nor, by .mesne assignments, -tofloppers Company, Inc.,

a corporation of Delaware lapplication February zama, sensi No. 417,240

` scams. (Casos-44) y..

This invention relates to piston rings and ex- Danders thereionand provides a novel arrangejmentof oil scrapingrings mounted two or more in a single ringfgroove with individual'expanders having ydiiierent expansive characteristics.

Most modern aircraft vengine .pistons carry six rings. Near the top are three compression rings Y o1' any suitable type. A short distance below the l lowermost of these, and above theplston pin', is a wide ring groove in which are mounted two oil scraping rings, the yso-called dual oil rings to4 which the present invention particularly applies. Farther down, on the skirt, is a single oil ring of suitable type. The dual oil rings may take dill'erent forms but a preferred iorm now in use will be illustrated in detail as typical. The upper one of the dual oil rings' wears faster, probably because it is lessl copiously lubricated than the lower. Hence it is proposed, according to the invention, to subject 7, .the lower ring to a greater expandingv action by diierentiating the expanders.

. 1satisfactorily accomplished by din'erentiating the rings. I

expanders with each other or with parts of the groove so that their undulation or crimps are stag lered. This is objectionable, because it impairsliredom of action and in some forms reyquiesi` the` notching of theexpanders, which is A'expensive and objectionable if the expanders are very narrow. Unless the notching ls carefully done, strain intensifying cracks will occur.

The invention provides an arrangement in which tlgexpanders are thin, narrow strips without notch or port; in which each expander is entirely free to shift circumferentially in the groove but cannot nest with the adjacent expander; and in which the expansive effects are readily diilerentiated. Adequate oil ilow past the expanders is inherently provided for.

For a complete understanding of theinvention, reference should be made to the accompanying drawing, in which:

Fig. 1 is a transverse section through the piston in the plane of the top of the dual ring groove.

Fig. 2 is a'fragmentary elevation showing the dual oil rings in the groove.

Fig. 3 is an enlarged section, axial with respect to the piston and showing dual oil rings and expanders in one groove. f y

This cannot be Fig. 4 is a perspective view of a fragment o f one of the rings looking from beneath and indicating the `form of oil seepage passage used.

Fig. 5 isa face view of the weaker expander (i. e. the upper in Figs. 1 and 3).

Fig. 6 is a. Aface view of the stronger expander.

Fig. '7 is a perspective view of the two expanders as they appear when unstressed. j

Y In the drawing. the piston I Il has acylinder contacting face Il withring groove I 3 vfrom the rear of, which the oil drainage ports I 4 lead to the interior 0f the piston.

In the groove I3 are mounted two split expansible oil scraping rings vIl and Il, which as Ausual are elastic vand so contoured, peened or otherwise contrived that they bear on the' cylinder wall throughout their circumierences and with 'pressures lwhich are uniform around their yentire circumi'erences, vso nearly as is practicable.

Each ring I5 or I6 has a cylindrical inner facer Il, a plane top face Il, and a plane bottom tace I 9 exceptI for the presence in the bottom face oi uniformly spaced shallow radial passages 2l provided for oil seepage.

The oil scraping rim 22 of the ring, the area which contacts the cylinder wall, lies between a convex fillet 23 towards the top, and an undercut groove 24 towards the bottom of the ring.

Theinner comers, at the junctions oi the cylindrical face Il with respectively the upper plane fEe/Icbottom face I8 are chamfered suf iiciently to prevent possible contact with adjacent expander as indicated lat 2B.

LEhese two expanders 2Q and 21 formed of thin, narrow strips of spring steel or other suitable material, viz. beryllium bronze are assembled edge to edge in groove I3 behind the rings. 'I'hey lnearly span the width of the groove I3' but have a free t therein. The signicant thing is that the expanders when unstressed are polygonal in form and are dissimilar as to the number of sides of their respective polygons. Simply as an example, the drawing illustrates one expander as approximately pentagonal and the other as approximately heptagonal.

The upper expander 2l is pentagonal, having iive crimps 28 and the lower expander 21 is heptagonal, havingv seven crimps 29. A generally polygonal contour, such as those: shown, is preferred, because expanders of such contour have demonstrated desirable spring characteristics in general use, but the invention imposes no limitation to the exact form.

The 'important thing is the differentiation in the number of crimps, and the consequent diii'erentiation in the number of enective spring units per expander. This accomplishes two valuable effects. The lower expander offers al greater exl padding eiect, and` can never nest with the upper (see Fig. 11) though eaclr expander is free to lmove Vcircumierentially in the groove I3.

The number of crimps to be used in each expander is a function of the expansive eiect desired and -whilea diierentiation by one or two crimps is commonly sumcient, anynumerical diflection may be based on the desired diierential tion of expansive actions, and a considerable range of control may be had.

By diierentiating the number of crimpsand -`l0 ferentiation will prevent nesting. Thus the seby properly selecting the form of the crimp, which also modiiies the elastic action to same degree,l quite precise selection of.v expansive action is pos- ,sible so that within limits, almost any result, so

tar as the comparative expansive eiects are concerned. is possible.

The invention imposes virtually no limitations on -the forni of the oil rings, uses expanders of .l

the simplest possible form, affords good oil ilow in the groove past the expanders, and permits latitude in design to secure the precise expansive eiects desired. The differentiation of expansive eiTect can be reduced nearly to the vanishing point when desirable while retaining the antinesting characteristic. To do this the two expanders `would be differentiated by only one 1. The combination of a piston having a ring asoqus groove; atleast two independently expansible rings mounted in said groove; and crimped expanders arranged edge to edge in the groove and contacting respective rings, said expanders being differentiated both in expansive action and in the number of crimps, whereby nesting is inhibited.

2. The combination ,ofa` piston havingv a ringv groove; at least two independently expansible rings mounted in said groove; and expanders formed of thin resilient strips of elastic material, crimped at intervals, each expander being of vaxial dimension "-not exceeding the axial dimension of the ring which it expands, and adjacent expanders `being diversiiied as to the numbers of crimps, whereby the expansive effects of adjacent expanders are diversiiied and nesting is inhibited. 3. The combination defined in claim 2 in which the. expanders are each free to move circumferentially in the ringgroove.

4. The combination defined in claim 2 in which .the crimps are so formedA that the expanders are approximately polygonal when free of stress, whereby they have long arcs of contact with the groove bottom when operatively stressed and good positioning edge-engagement between expanders is assured.

5. A multiple expander for use in a single ringgroove comprising at least two independent expanders formed eachof a thin resilient strip of elastic material crimped at intervals to assume a substantially polygonal form when unstressed, the expanders being arranged edge to edge in the groove and adjacent polygonal expanders being diversied as to the number of sides whereby nesting is inhibited, the expanders being free to move independently in the direction of the circumierence of the groove.

ALLEN W. MORTON. 

